NEW YORK (CBSNewYork/AP) — Smoke inhalation and thermal burns caused the death of a New York City firefighter who perished in a cluttered public housing high-rise apartment fire in Brooklyn.

A spokeswoman for the New York City medical examiner’s office said Monday the manner of Lt. Gordon “Matt” Ambelas’ death still was under investigation.

Fire officials said the 40-year-old FDNY veteran was overcome with smoke and flames while searching for possible victims Saturday at the Independence Towers on Wilson Street in Williamsburg.

A preliminary investigation showed a pinched electrical cord in a cluttered apartment started the blaze on the 19th floor of the 21-story building, fire officials said Sunday.

Flames quickly spread to the 17th and 18th floors. Ambelas was among the first firefighters in the building.

Fellow firefighters found Ambelas unconscious and carried him out of the building. They worked with emergency rescuers to try to revive him, but he died at a hospital, Mayor Bill de Blasio said.

“New York has suffered a terrible and tragic loss,” de Blasio said Sunday. “We all mourn his loss, and I ask every New Yorker to keep Lt. Ambelas and his family in their thoughts and prayers.”

“It’s a moment that we in the Fire Department all dread when we lose one of our family,” Fire Commissioner Daniel Nigro said. “But Lt. Ambelas died doing what fire officers do — leading firefighters in search for life.”

Angel Pagan, the tenant in apartment 19B, denied to CBS 2 that his apartment was cluttered.

Officials have declined to detail what happened inside the apartment, citing the ongoing investigation.

Meanwhile on Monday, as CBS 2’s Dave Carlin reported, family and friends could not believe Ambelas was gone.

Family and friends said Ambelas’ life of fighting fires and saving lives was constant in a stellar, decorated 14-year career. But they said love for family was what he really lived for.

“He died a hero — that’s how he lived,” he said. Ambelas, he added, was “truly one of the best human beings that anyone would ever want to meet.”

Ambelas had been promoted to lieutenant 10 months ago. Throughout a 14-year career he helped the city through its darkest hours, including the recovery from the Sept. 11, 2001, terrorist attacks and Superstorm Sandy.